1. Field of the Invention
This invention relates to integrated circuit devices and more particularly to emulator systems of complex single chip integrated circuits such as microprocessors or microcomputers.
2. Description of the Prior Art
The fabrication of electronic devices on semiconductor substrates allows for the miniaturization of electronic components. The advantages of such miniaturization not only includes the savings of weight and volume but additionally, miniaturization provides for lower power consumption by the semiconductor electronic devices. As the art of semiconductor manufacturing becomes more mature, the number of electronic devices that are placed on a semiconductor substrate increases. The complexity of semiconductor integration progressed from small integration to medium scale integration and finally to large scale integration. At this time the next step is very large scale integration (VLSI). As the number of electronic devices contained on a single semiconductor substrate increases, the complexity of the functions accomplished by these devices increases. In the early stages of semiconductor integration, a single chip might contain four dual input NAND gates to perform single logic functions. Integrating chips at this level of complexity is relatively simple because by monitoring the inputs and outputs of the chips, the designer is able to tell if the chip was operating properly and further is able to reasonably predict the output for different input states. As circuits contained on the single semiconductor substrate became more complex, monitoring the signals into and out of the chip did not always permit the designer to see exactly what was happening within the electronic devices on the chip.
With the introduction of microprocessors, system testing and system development became fairly complex. Microprocessors not only contain a large number of electronic devices on a single semiconductor chip but also contain electronic devices that are programmable. This allows the designer to program the semiconductor device in order to perform certain desired functions. With this capability, however, the designer also needs the capability to monitor the internal performance of individual electronic devices contained on the semiconductor chip in order to determine if the program that is in the microprocessor or microprocomputer will accomplish its intended function. Recently, microprocessor and microcomputer development systems have been marketed to perform this function. These development systems supply the designer with what seems to be the microprocessor or microcomputer that is contained on a semiconductor chip. In actuality, the microprocessor or microcomputer is being emulated by a set of individual semiconductor devices of a smaller complexity tied together in such a manner as to emulate at least a portion of the operations of the microprocessor or microcomputer. In addition to the emulation capability, the development system also provides the user with the ability to view data that is contained internally in the microprocessor together with certain control functions to allow the user or designer to control the operation of certain portions of the microprocessor or microcomputer in order that they may observe the operation of the microprocessor or microcomputer while executing different user defined programs. In this manner, the designer may determine the behavior of the microprocessor or microcomputer when executing a designer's specified program. Therefore the designer uses the development system to develop software to be installed or fabricated in the microprocessor or microcomputer so that the microprocessor or microcomputer will then function as the designer desires.
Several development systems are currently available for developing software for a variety of microprocessors and microcomputers. All of these development system, however, suffer from the same disadvantage; they do not actually contain the microprocessor or microcomputer in its final form that is emulated. They merely simulate the hardware of these devices. This may result in problems when the software developed is later fabricated in the actual chip. These problems may arise from differences in timing or signal characteristics between the devices of the emulator and the internal devices on the chip.
This invention employs interconnection techniques that have existed in semiconductor technology. U.S. Pat. No. 3,577,038 entitled "Semiconductor Devices" by Charles R. Cook assigned to Texas Instruments Incorporated includes the description of the interconnection of semiconductor devices on the semiconductor substrate. Another source of teaching is U.S. Pat. No. 3,643,232 entitled, "Large Scale Integration of Electronic Systems and Microminiature Form" by Jack S. Kilby, filed Dec. 21, 1964, assigned to Texas Instruments Incorporated.